Control systems for a rail-bound driving robot and procedures to operate

ABSTRACT

A process for the control of movement of rail-based automated transport vehicles ( 2   a,    2   b ) in a multi-branch rail system ( 1 ) that contains in particular switches ( 4 ), lifts ( 10, 11 ) and other integrated rail-based units, including stations for loading and unloading, with a depiction of rail system ( 1 ) in the control system of the automated transport vehicle ( 2   a,    2   b ) with all integrated rail-based units ( 4; 10, 11; 13 - 16; 20, 21, 33 ) by means of nodes ( 7 - 9; 22 - 25 ) and edges ( 26 - 31 ) as defined in graph theory.

The invention concerns a control system for rail-based automatedtransport vehicles and a process for its operation as described in thepreamble of Patent Claim 1.

EP 1 703 351 A2 describes a system known as a “Manhattan System” for acontrol system for rail-based automated transport vehicles with amulti-branch rail system. This control system consists of a designationof a number of one-way streets, intersections, and traffic rules thatpreclude a collision of multiple automated transport vehicles operatingin a rail system. The present invention refers to the informationcontained in that document, and such information is an integralcomponent of this description.

The same applies to the object of DE 198 42 752 B4, which describes atransfer system comparable to the rail system of the invention.

The designation as “Manhattan System” was derived from the street systemin Manhattan in the city of New York, where traffic rules are imposed bya strict road management system; for example, that traffic may drive onroads leading from West to East only in that direction, whereas trafficon roads leading in the opposite direction may drive only in theopposite direction.

This set of traffic rules assures collision-free travel for a number ofrail automated transport vehicles in a rail system.

However, the known system has the disadvantage that it is not feasibleto specify multiple levels of the rail system. Thus, it is atwo-dimensional system operating on a single horizontal plane, whichimposes restrictions.

Thus, the present invention is designed to provide a control system forautomated transport vehicles running on a multi-branch rail systemoperating on multiple horizontal planes.

Emphasis shall be placed on the speedy derivation of controlinstructions, on minimal computation effort, and on an independentderivation process of the intended travel route for each automatedtransport vehicle with advance planning for multiple intersections andplanes.

The Manhattan System limits the derivation for multiple paths to theapplication of traffic rules, which is an inflexible process. Thus, ifthe rules for a particular rail segment are changed, the entire softwarehas to be modified.

The present system has the advantage that an automated transport vehiclewith a built-in control system can determine its future routing via aplurality of intersections and switches by use of a virtual evaluationsystem.

It is an essential characteristic of the invention that the rail systemis depicted in the control system of the automated transport vehicle bymeans of nodes and edges as defined in graph theory. This depictionpresents a directed graph. A complete and multi-branch rail system withits features, work stations and storage sites is thus unambiguouslydescribed by a list of nodes and their associated edge listings.

This provides the advantage that each automated transport vehicle candetermine its current destination in advance prior to initiatingmovement, where the route is derived by a virtual evaluation system thatis comparable to a benefit-cost analysis.

The various lines to be traveled by the automated transport vehicle arelinked to virtual costs. Costs of reaching a distant destination fromthe current location are increased by increasing the distance to betraveled by the vehicle and by increasing the number of planes to betraversed.

Graph theory defines a graph as a number of nodes (also called vertices)with a number of edges. An edge here includes exactly two nodes. If thenumber of nodes is finite, the graph is called a finite graph; thealternative is an infinite graph. If the edges are described as pairs ofspecific nodes, the graph is described as a directed graph. In thatinstance, a distinction is made between edge (a, b)—the edge from node ato node b—and edge (b, a)—the edge from node b to node a.

Nodes and edges may also be designated by color (expressed formally innatural numbers) or weights (i.e. rational or real numbers). Such graphsare designated as node or edge colored graphs or node or edge weightedgraphs.

Graphs may have various properties. For example, a graph may becontiguous, bipartite, planar, Eulerian or Hamiltonian. Queries may beentered for the existence of specific separate graph segments or forcertain parameters, such as the number of nodes, the number of edges,the minimum degree, the maximum degree, the width at the narrowestpoint, the diameter, the number of associated nodes, the number ofassociated edges, the chromatic parameter, the stability parameter orthe number of groups.

The various properties may be correlated. Graph theory is designed toexamine these relationships. For example, the number of associated nodeswill never exceed the number of associated edges, which in turn willnever exceed the minimum degree of the graph in question. For levelgraphs, the number of colors will always be less than five. This isknown as the Four Color Theorem.

Some of the graph properties listed can be determined algorithmicallyquite quickly, such as that the effort will not expand faster than thesquare of the size of the graphs.

The following definitions apply to a use of graph theory to thecharacteristics of the invention:

Route: Several edges yield a route

Nodes: Nodes may be embodied as lifts, switches, RFID tags or a segment

Edges: Edges are connections between two nodes

Location: For example, location may designate a storage location in awarehouse

Nodes are thus positions where an action is required. Normally, suchpositions will include an RFID tag (such as registration for a lift, aloading station and the like). But it is also possible to set virtualnodes (without an RFID tag).

Node IDs 1 and 2 are defined for the automated transport vehicle itself,and node IDs 1 and 2 are used for internal processes, such as thecontrol of the lift supported by the vehicle, for a loading device orfor other items on the vehicle designed to load or unload the vehicle,for example.

Virtual nodes are nodes without an associated RFID tag on the track.

A. Virtual nodes are used for:

a.) Save real (physical) RFID tags:

In order to keep matters simple, real RFID tags will be used only onceon the loading platform of a lift. Thus, each level has then one virtualnode with one virtual RFID tag in order to indicate entry into a newstorage system.

b.) Positions in close proximity:

RFID tags operating with radio transmissions need to be separated by acertain distance in order to send an unambiguous signal to identify thesending tag in a line of tags in close proximity. It is feasible to seta single RFID tag and to include a second node as a virtual node. Thatapproach precludes crossing signals from RFID tags located in closeproximity.

c.) Dead ends:

The dead end of a line in a warehouse will be designated by a virtualnode. This permits the identification of an edge at the end of a storagerange without using an RFID tag and likewise to specify a certaindefinition of the length of the storage range.

B. Information of a node:

a.) Unambiguous node ID (size 1, less than 65535)

b.) Node type: Each node may be of several types simultaneously (such aslift, registration for lift, stop at lift and the like)

c.) RFID number of the associated RFID tag (virtual nodes have the RFIDnumber 0)

C. Edges

a.) Edges define the path from one position to the next.

b.) Each edge links two nodes and signifies an unambiguous directionfrom one node to the next.

C1. Edges in a storage site within a warehouse:

Edges depicting a path in a warehouse will store the number of storagesites to the right and to the left of the path (seen from the maindirection of travel of the automated transport vehicle). It is importantin the case of a dead-end path or a path that can be accessed in twodirections that the numbers be stored for only one of the edges(preferably for the edge pointing in the direction of travel).

C2. Length of the edge:

This is the distance of the path between two nodes (larger than zero andless than 65534 cm).

D. Costs:

The costs of a virtual evaluation system may range from 0 to 255, where0 implies that the path is deactivated.

The longer the path, the higher the costs implied by taking this path.

Similarly, costs for the paths are allocated to each path based on thelayout in the system.

For example, a high cost accrues for travel from an upper or lower levelin the storage system to a different level. The costs are thus alsocorrelated with the travel time required between the start and thedestination as well as with the changes in levels en route.

Thus, a change in levels will occasion higher costs than a direct paththat does not require a change in levels.

Cost management is currently imposed only for the lift and for thecontrol of movement towards a lift. However, the invention is notlimited by that facet. The invention may distribute and assign costs forany edge in order to derive a certain valuation for a specific path.

Rather than the term “costs,” other evaluation terms may be used aswell, such as “points” or other virtual parameters that can be valued ina decimal system.

The present invention has the advantage that the automated transportvehicle will note its current location for any location of the vehiclevia a NFC connection (all RFID tags of the invention operate only in theNFC field). The transmission is handled by passive HF RFID tags asdescribed in ISO 14443 or ISO 15693).

The NFC technology operates at a frequency of 13.56 MHz and offers adata transmission rate of no more than 424 kBit/s for a transmissionrange of only ten centimeters. The communication between NFC devices maybe either active-passive or active-active (Peer-To-Peer) unlikeconventional wireless transmissions on this frequency (onlyactive-passive). Thus NFC provides a linkage to the RFID world.

NFC communications achieve a range of roughly 10 to 30 cm, whichrequires the automated transport vehicle to approach closely to any RFIDtag along the path and to initiate contact with the RFID tag in order tocompute its travel route.

The data exchange with the RFID tag via the NFC protocol then indicatesthe current position of the vehicle.

The vehicle then uses a wireless protocol, such as the ZigBee standard,to transmit a signal to an external control unit regarding its presentposition and also queries simultaneously for any pending orders. ZigBeeis an industry standard for wireless networks. The PHY and MAC layersare based on IEEE 802.15.4 which facilitates transmissions betweenhousehold appliances, sensors and the like over short distances (10 to100 meters).

This wireless communication connection then transmits transport andmovement orders to the automated transport vehicle.

These transport and movement orders also specify the destination ofmovement.

The computer of the automated transport vehicle then computes thecurrently optimal path towards that destination. The edges are read intothe computer of the automated transport vehicle for a subsequentevaluation of the path using all edges, specifically based on theaggregate costs.

As a result, the automated transport vehicle will have a number ofoptions to reach the intended destination.

It is advantageous that the automated transport vehicle chooses theroute of lowest costs. This also implies that a change of levels will beavoided to the extent possible, that the route is chosen to avoidblocked pathways, and that needed detours will be considered. The(path-specific) costs are determined in this manner.

The system is a vector-based navigation system, where each RFID-basednode has a unique geographic position. The information consists of atleast one edge, a corner and information regarding the level.

The layout of the entire rail system is stored in each case in thecomputer of the automated transport vehicle as a map file describing aplurality of nodes and edges. Thus, the computer contains allinformation needed to reach any given point in the multi-branch railsystem.

This is similar to a vector graphic system as provided in any motorvehicle and in the navigation system in that motor vehicle, but thesystem of the invention also needs to track a plurality of levels andthe costs associated with all edges as a function of the level and thedistance from the current position.

This is not a geo-referenced GPS system as is required for aconventional navigation system, but there are only RFID nodes in keypositions of the rail system (switches, entrance, exit, lift, exit fromthe warehouse, designation of the storage level) that communicate overshort distances (NFC) with the automated transport vehicle. This avoidsthe undesirable interference of multiple signals for adjacent RFIDnodes. Thus, such RFID signals may be free of interference despite closeproximity.

Furthermore, the invention has the advantage that virtual RFID nodes maybe defined. This has the added advantage that a physical tag is notrequired and that a virtual (added) RFID tag is merely added to aphysical RFID tag, which designates, for example, the distance from thevirtual node to the real RFID tag, the level and other path-specificcriteria.

Thus, for any physical RFID tag, a plurality of virtual RFID tags may bedefined for the vicinity of this real RFID tag.

This has the advantage that virtual RFID tags may be positioned in closeproximity to an RFID tag without encountering undesirable interferencewith physical RFID tags, as would be the case for physical RFID tags inclose proximity.

As a result, the control system incorporated into the automatedtransport vehicle notes the current location of the vehicle in themulti-branch rail system by accepting the unambiguous identification ofthe closest RFID tags and comparing it to the multi-branch rail systeminformation in memory to confirm the current location.

Based on this information on the current position, the evaluationsoftware then decides on the optimal path to the destination.

It is important that no additional data need to be stored on the RFIDtag, except for the unique ID number, which thus minimizes thecomputational effort.

However, the invention is not limited in this regard, because theinvention could also designate that an RFID tag sends not only itsunique position to the automated transport vehicle, but also additionaldata, such as movement instructions, transport instructions, cost dataand the like.

The inventive object of the present invention derives not only from theseparate patent claims, but also from the combination of the variouspatent claims.

All of the information and characteristics shown in the documentation,including the summary, and including specifically the spatial layoutshown in the figures, are claimed as essential to the invention to theextent that they are novel individually or in combination relative tothe state of the art.

The invention will be described in more detail in the following byreference to the figures, which show merely one embodiment. Essentialcharacteristics and advantages of the invention are presented in thefigures and their descriptions.

They show:

FIG. 1: A schematic top view of a rail system with an automatedtransport vehicle operating in that rail system.

FIG. 2: A frontal view of a multi-branch rail system with a storagesystem containing four storage levels above each other, where lifts areincluded at the entrances and exits to such storage levels.

FIG. 3: A schematic of the frontal view of a lift with two automatedtransport vehicles on a lift platform and edges marked with directionalarrows and associated virtual costs.

FIG. 1 shows a schematic top view of a multi-branch rail system 1 onwhich automated transport vehicle 2 a moves in the direction depicted byarrow 3.

The vehicle enters switch 4. Switch 4 branches into two rails 5, 6.

Automated transport vehicle 2 contains an RFID reader 36 that uses NFCtransmission 32 to make contact with RFID node 7, which is the closestnode in the direction of travel on rail system 1.

RFID node 7 sends its unique ID and a ping via the NFC connection. TheID is entered into the control system of the automated transport vehicleand is compared there to the information about the rail system, suchthat the ID of RFID node 7 will yield the current location of theautomated transport vehicle 2 a in rail system 1 with a precision of 20cm.

The exits from switch 4 include the additional RFID nodes 8 and 9. Asautomated transport vehicle 2 a approaches one of these nodes 8, 9, anew NFC connection is made between reader 36 in automated transportvehicle 2 a and the respective node 8, 9, and the now current positionis noted from the evaluation of the ID of this RFID node 8, 9.

Automated transport vehicle 2 a can then move in the direction of arrow3 a or 3 b along the corresponding rail path 5 or 6.

FIG. 2 shows a frontal view of the multi-branch rail system. The view issimplified to show that the entrance to multi-branch storage system 12includes two vertical lifts 10, 11.

Each lift 10 supports at least one lift platform 20, 21, with which oneor more automated transport vehicles 2 a, 2 b may be raised or loweredin order to move in the direction of arrow 17 or in the oppositedirection from the lower level of rail system 1, 5, 6 to a higherstorage level 13-16 of storage system 12.

The paths between the RFID nodes of the entire storage system 12 aredefined by edges 26-31. Each edge has a determinate length withassociated virtual costs.

The concept of virtual costs was discussed in the general description.

For example, a first edge 26 or optionally a second edge 27 extends fromRFID node 7 to RFID node 22 or 23 on lift platform 20.

In the embodiment depicted here, lift platform 20 supports two RFIDnodes 22, 23, because lift platform 20 is intended to transport twoseparate automated transport vehicles 2 a, 2 b, as shown in FIG. 3,where each automated transport vehicle follows its own path andtransport orders.

By analogy, other edges are formed by the distance from RFID nodes 22,23 to RFID nodes 24 a, 24 b, 24 c and 24 d on the storage level sides.

Additional edges are formed by edges 29 on storage levels 13-16. Otheredges are formed by edges 28 a and edges 30 and 31, which are defined onthe exit side of storage system 12 in the direction of lift 11 at theexit.

Thus, each automated transport vehicle may move independently of anyother automated transport vehicle in each case on one storage level13-16 in the direction of arrows 18 or 19.

The distances between RFID nodes 22-25 are defined by the correspondingedges, where each edge has an associated virtual cost.

FIG. 3 shows an example of the computation of the cost of movement fortwo independent automated transport vehicles 2 a, 2 b positioned on liftplatform 20 of lift 10, 11.

For simplicity, the RFID nodes are identified with single digit numbersin a circle. Thus, these numbers are not reference numbers, but nodenames.

For example, if automated transport vehicle 2 a is in position on liftplatform 20 and initiates an NFC connection with node No. 5 (RFID node22), the distances to any number of nodes along a path will be computed.

For example, if automated transport vehicle 2 a moves from node No. 1 tonode No. 3 via rail 5, the vehicle will receive a first path instructionfrom node No. 3 in the form of edge 34 with costs of 255.

Thus, edge 34 extends from node No. 3 to node No. 5.

If the automated transport vehicle 2 a is intended to move from node No.3 via node No. 5 to node No. 6 (node No. 6 is RFID node 23), additionalcosts will be incurred, but at a low rate of decimal 1.

In contrast, if automated transport vehicle 2 a is intended to movedirectly from node No. 3 and node No. 27 (RFID node 24 c)straight-through on the same level of raised lift platform 20, this edgewould also have a cost of only 1.

These costs are so low, because no movement to a different level isrequired.

Thus, it is feasible to move from node No. 1 via node No. 3 and node No.7 to node No. 10 at minimal cost given a direct movement via the edgesalong the path. This path will then be the preferred routing for theautomated transport vehicle.

It is thus feasible to specify the costs to be incurred by movement ofautomated transport vehicle 2 a, 2 b from node No. 5 or node No. 6 toany distant node by tracing the arrows and the associated costs for theintervening edges.

FIG. 3 also shows that the lift may also include a processing unit 33and that only minimal costs of 1 would be incurred, if the route were tolead from lift 20 to nodes No. 13, 14 or 15.

However, if the route were to require movement to node No. 9, whichforms the discharge of lift 10, 11, high costs of 255 would be incurred,because it involves a change in levels to storage level 16, which formsthe lowest level of storage system 12.

LEGEND ON FIGURES

-   1 rail system-   2 a Automated transport vehicle-   2 b Automated transport vehicle-   3 Direction of arrow-   4 Switch-   5 Rail-   6 Rail-   7 RFID node-   8 RFID node-   9 RFID node-   10 Lift-   11 Lift-   12 Storage system-   13 Storage level-   14 Storage level-   15 Storage level-   16 Storage level-   17 Direction of arrow-   18 Direction of arrow-   19 Direction of arrow-   20 Lift platform-   21 Lift platform-   22 RFID node-   23 RFID node-   24 RFID node a, b, c, d-   25 RFID node a, b, c, d-   26 Edge-   27 Edge-   28 Edge-   29 Edge-   30 Edge-   31 Edge-   32 NFC connection (RFID)-   33 Processing unit-   34 Edge-   35 Edge-   36 RFID reader

1. A process for the control of movement of rail-based automatedtransport vehicles in a multi-branch rail system that contains inparticular switches, lifts and other integrated rail-based units,including stations for loading and unloading, characterized by having adepiction of rail system in the control system of automated transportvehicle with all integrated rail-based units by means of nodes and edgesas defined in graph theory.
 2. The process of claim 1, characterized byhaving each node associated with an RFID tag.
 3. The process of claim 2,characterized by having the RFID tag depicted in the control system aseither a physical RFID tag or as a virtual RFID tag with no physicalproperties.
 4. The process of claim 1, characterized by havingrail-based units defined as nodes, where the edges form the connectionsbetween nodes.
 5. The process of claim 1, characterized by havingvirtual costs defined for each path to be travelled by automatedtransport vehicle, where such costs are a measure expressing the easeand/or speed by which a target can be reached.
 6. The process of claim1, characterized by having the automated transport vehicle compute itspath by several steps, where the first step is that the vehicleapproaches any RFID tag along the path and initiates communication withthe RFID tag, where the second step is that the vehicle learns itscurrent position by a data exchange with the RFID tag by means of theNFC protocol, where the third step is that the vehicle sends a signal toan external control to indicate its present position by means of awireless protocol, such as the ZigBee standard, where the fourth step isthat the vehicle queries the external control whether there are anycurrent orders for movement for the vehicle, where the fifth step isthat the automated transport vehicle receives an order for transport andmovement with specification of the destination via the wirelesscommunication with the external control unit, where the sixth step isthat the automated transport vehicle reads the edges and nodes of thedestination and undertakes an evaluation of the optimal path towardsthat destination by reference to the rail system information stored inthe automated transport vehicle, where the evaluation compares allalternative paths towards the destination, and where the seventh step isthat the automated transport vehicle selects the path to the destinationwith the optimal evaluation regarding the costs of movement.
 7. Acontrol system to control the movement of rail-based automated transportvehicles in a multi-branch rail system that contains switches, lifts andother rail-based units, including specifically loading and unloadingstations, characterized by having a depiction of rail system in thecontrol system of the automated transport vehicle with all integratedrail-based units by means of nodes and edges as defined in graph theory.8. The control system of claim 7, characterized by having eachrail-based unit of rail system equipped with an RFID tag thatcommunicates with an RFID reader in automated transport vehicle via anNFC connection.
 9. The control system of claim 7, characterized byhaving a geographical definition for each RFID-based node that notes atleast one edge, one corner and information on the level of the node. 10.The control system of claim 7, characterized by having the layout of theentire rail system (1) stored in the computer of the automated transportvehicle as a complete map described by a plurality of nodes and edges.11. The process of claim 2, characterized by having rail-based unitsdefined as nodes, where the edges form the connections between nodes.12. The process of claim 3, characterized by having rail-based unitsdefined as nodes, where the edges form the connections between nodes.13. The process of claim 2, characterized by having virtual costsdefined for each path to be travelled by automated transport vehicle,where such costs are a measure expressing the ease and/or speed by whicha target can be reached.
 14. The process of claim 3, characterized byhaving virtual costs defined for each path to be travelled by automatedtransport vehicle, where such costs are a measure expressing the easeand/or speed by which a target can be reached.
 15. The process of claim4, characterized by having virtual costs defined for each path to betravelled by automated transport vehicle, where such costs are a measureexpressing the ease and/or speed by which a target can be reached. 16.The process of claim 2, characterized by having the automated transportvehicle compute its path by several steps, where the first step is thatthe vehicle approaches any RFID tag along the path and initiatescommunication with the RFID tag, where the second step is that thevehicle learns its current position by a data exchange with the RFID tagby means of the NFC protocol, where the third step is that the vehiclesends a signal to an external control to indicate its present positionby means of a wireless protocol, such as the ZigBee standard, where thefourth step is that the vehicle queries the external control whetherthere are any current orders for movement for the vehicle, where thefifth step is that the automated transport vehicle receives an order fortransport and movement with specification of the destination via thewireless communication with the external control unit, where the sixthstep is that the automated transport vehicle reads the edges and nodesof the destination and undertakes an evaluation of the optimal pathtowards that destination by reference to the rail system informationstored in the automated transport vehicle, where the evaluation comparesall alternative paths towards the destination, and where the seventhstep is that the automated transport vehicle selects the path to thedestination with the optimal evaluation regarding the costs of movement.16. The process of claim 3, characterized by having the automatedtransport vehicle compute its path by several steps, where the firststep is that the vehicle approaches any RFID tag along the path andinitiates communication with the RFID tag, where the second step is thatthe vehicle learns its current position by a data exchange with the RFIDtag by means of the NFC protocol, where the third step is that thevehicle sends a signal to an external control to indicate its presentposition by means of a wireless protocol, such as the ZigBee standard,where the fourth step is that the vehicle queries the external controlwhether there are any current orders for movement for the vehicle, wherethe fifth step is that the automated transport vehicle receives an orderfor transport and movement with specification of the destination via thewireless communication with the external control unit, where the sixthstep is that the automated transport vehicle reads the edges and nodesof the destination and undertakes an evaluation of the optimal pathtowards that destination by reference to the rail system informationstored in the automated transport vehicle, where the evaluation comparesall alternative paths towards the destination, and where the seventhstep is that the automated transport vehicle selects the path to thedestination with the optimal evaluation regarding the costs of movement.17. The process of claim 4, characterized by having the automatedtransport vehicle compute its path by several steps, where the firststep is that the vehicle approaches any RFID tag along the path andinitiates communication with the RFID tag, where the second step is thatthe vehicle learns its current position by a data exchange with the RFIDtag by means of the NFC protocol, where the third step is that thevehicle sends a signal to an external control to indicate its presentposition by means of a wireless protocol, such as the ZigBee standard,where the fourth step is that the vehicle queries the external controlwhether there are any current orders for movement for the vehicle, wherethe fifth step is that the automated transport vehicle receives an orderfor transport and movement with specification of the destination via thewireless communication with the external control unit, where the sixthstep is that the automated transport vehicle reads the edges and nodesof the destination and undertakes an evaluation of the optimal pathtowards that destination by reference to the rail system informationstored in the automated transport vehicle, where the evaluation comparesall alternative paths towards the destination, and where the seventhstep is that the automated transport vehicle selects the path to thedestination with the optimal evaluation regarding the costs of movement.18. The process of claim 5, characterized by having the automatedtransport vehicle compute its path by several steps, where the firststep is that the vehicle approaches any RFID tag along the path andinitiates communication with the RFID tag, where the second step is thatthe vehicle learns its current position by a data exchange with the RFIDtag by means of the NFC protocol, where the third step is that thevehicle sends a signal to an external control to indicate its presentposition by means of a wireless protocol, such as the ZigBee standard,where the fourth step is that the vehicle queries the external controlwhether there are any current orders for movement for the vehicle, wherethe fifth step is that the automated transport vehicle receives an orderfor transport and movement with specification of the destination via thewireless communication with the external control unit, where the sixthstep is that the automated transport vehicle reads the edges and nodesof the destination and undertakes an evaluation of the optimal pathtowards that destination by reference to the rail system informationstored in the automated transport vehicle, where the evaluation comparesall alternative paths towards the destination, and where the seventhstep is that the automated transport vehicle selects the path to thedestination with the optimal evaluation regarding the costs of movement.19. The control system of claim 8, characterized by having ageographical definition for each RFID-based node that notes at least oneedge, one corner and information on the level of the node.
 20. Thecontrol system of claim 8, characterized by having the layout of theentire rail system (1) stored in the computer of the automated transportvehicle as a complete map described by a plurality of nodes and edges.